The objective is to identify and characterize genetic variation in mice for regulatory and structural loci. We have drawn extensively from a diverse sampling of the mouse gene pool by obtaining mice from different geographical regions of the world. Taxonomically, these mice have included house mouse Mus species which are geographically separated but will readily interbreed with laboratory mice. It has also included mouse species trapped in field habitats in Eastern and Western Europe, M. Horbulanus and M spretus, which do not interbreed in the wild but do hybridize with laboratory strains in animal colony conditions. We have also sampled mouse species of the genus Mus which do not interbreed in the field or under laboratory conditions. These resources are currently maintained in breeding colonies at Roswell Park and they have supplied us with an extensive array of genetic variation for gene structure and regulation which is not present among the strains of laboratory mice. We have used resources to identify regulation of gene expression at the level of synthesis and processing of gene products. This proposal describes experimental approaches for extending that work and for characterizing the biochemical and molecular basis of genetic variation for the regulation of glucuronidase expression in subcellular localization and in the kidneys of testosterone treated mice. We are concerned with characterizing the molecular elements involved in gene regulation which act cis. In particular, we would like to known whether developmentally and hormonally regulated genes including, Beta-glucuronidase, RP-2 and Odk, are cis regulated at the level of transcription or RNA stabilization. We have observed substantial differences between Mus species in the hormonal regulation of several genes in mouse kidney. we have proposed experiments to test whether genetic variation is present among Mus species for trans acting regulatory elements and, if so, to characterize the expression of these genes and map them on the mouse gene map. This proposal also extends our use of chemical and X-ray mutagenesis to produce mutations in specific gene products. Experimental approaches are detailed to identify mutations on the X chromosome as well as for autosomal genes. X-chromosome mutations will be recovered for X-chromosome disorders in mice which model disorders of medical concern in humans. A method is proposed for testing mosaic expression of X-chromosome genes in heterozygous females. It provides a simple, economical test which can identify mutational events at up to 100 loci on the X chromosome using a single biochemical assay.